In the Space Shuttle main engine hydrogen and oxygen turbopumps, a shaft coupled between a turbine and a high volume pump is spun by the turbine at a high rate of speed, with the liquid hydrogen, or fuel pump, turning in excess of 37,000 rpm and the liquid oxygen, or oxidizer, pump turning at about 27,000 rpm. The shaft coupling the turbine section and the pump section transfers energy sufficient to pump liquid oxygen or liquid hydrogen at flow rates of several thousand gallons per minute to the engines. In the liquid oxygen turbopump, this shaft is rotatably supported by antifriction bearings, a roller bearing and ball bearing at one end of the shaft, and a single, larger ball bearing near the opposite end of the shaft. These bearings operate in a cryogenic environment with little or no lubricant, requiring liquid oxygen flow through the bearings in order to prevent them from being destroyed. The large ball bearing is provided with an inner race constructed of two annular portions each fixed, as by an interference fit, to an extension of a preburner impeller, in turn splined to the shaft, a cage to maintain separation of the balls of the bearing, and an outer race fixed, again, as by an interference fit, in an outer race bearing carrier fitted in an opening, or support configuration, in the turbopump housing.
In order to balance axial loads, or thrust, applied to the shaft, a system has been developed wherein small axial movements of the rotor and shaft due to turbine thrust are utilized to regulate a flow of liquid oxygen that in turn controls axial position of the rotor and shaft. This allowable axial movement of the shaft is facilitated at the single, large bearing in part by constructing the bearing to allow slight axial movement between the inner race and balls of the bearing. Additionally, a gap known as a deadband gap is provided between the outer race carrier within which the outer race is held, and the carrier support configuration interfacing the outer race carrier and the housing of the turbopump. This deadband gap provides a clearance within which the outer race carrier and outer race may axially move in order to accommodate axial movement of the shaft and is sized at about 0.002". With this gap sizing, springrate, which is a measure of rigidity of the support configuration, is maintained at a relatively high value, minimizing radial deflections of the support configuration. However, slope, or uneven radial distortions along the axis of the support configuration and outer race carrier due to fluid pressure against the turbopump housing adjacent the bearing, and occurring particularly when power level settings are changed, may bind the circular bearing carrier in the support configuration. This axial restraint may cause an overload condition of the bearing, resulting in bearing failure.
Another problem in the prior art is that, while a restraining shear pin prevents the outer race carrier from spinning in the housing support, dynamic tests have shown that torque applied to the outer race carrier occasionally exceeds the shear strength of the pin, resulting in the pin shearing and the outer race carrier being spun in its support. Further, flow of liquid oxygen through the bearing occasionally exceeds design parameters, which can apply unacceptable side loads on the ball bearing cage and cause the cage to incur damage. Any of the aforementioned problems may cause damage, necessitating expensive and timeconsuming repairs to the turbopump.
Accordingly, it is an object of this invention to provide an outer race carrier and support configuration therefor that desensitizes these components to bearing support springrate, bearing support operational slope, and excessive flow of liquid oxygen through the bearing.